Television intercarrier or sound receiver circuit



Feb. 2l, 1950v G. w. FYLER 2,498,488

TELEVISION INTERCARRIER 0R SOUND RECEIVER CIRCUIT Filed June 14, 1946 2 Sheets-Sheet l f/ Fi 4 Y Y f f ff 9 ,f f l s Inventor: George W. Fyl er;

bym @m H S Attofvw ey.

Feb, 21, 1950 G. w, FYLER 2,498,488

TELEVISION INTERCARRIER 0R SOUND RECEIVER CIRCUIT Filed June 14, 1946 2 Sheets-Sheet 2 Inventor: George VV. Vy Ier,

bym am His Attorney.

Patented Feb. 21, 1950 TELEVISION INTERCRRIER OR SOUND RECEIVER CIRCUIT George W. Fyler, Lombard, Ill., assigner to General Electric Company, a corporation of New York Application June 14, 194,6, Serial No. 676,651

4 Claims.

My invention relates to high frequency circuits of the type employed in television receivers and it has for its primary object to effect certain improvements in television receiver circuits for translating simultaneously a plurality of signals variable over different bands of frequencies.

In the usual television receiver, it is customary to employ two intermediate frequency channels to translate separately the intermediate frequency Waves modulated by the video and audio signals. In a conventional television circuit, the channel for the video modulated intermediate frequency wave has a relatively broad band width characteristic. The other channel has a comparatively narrow 4band width characteristic and is used to translate the audio modulated frequency wave.

Each channel, furthermore, requires separate detectors and subsequent amplifiers for satisfactory reproduction of the modulating signals. In order to provide advantages both in operational characteristics and in design and cost, it is an object f my invention to provide a new and improved television receiver which employs a single intermediate frequency channel for translating both video and audio modulated carrier waves.

It is still another object of my invention to provide a new and improved television receiver circuit in which heterodyning of the video and audio modulated intermediate frequency waves is utilized to produce an additional audio modulated carrier wave for subsequent reproduction of the audio signals.

It is a still further object of my invention to provide a new and improved television receiver circuit which employs a single channel for normally translating both video and audio modulated carrier waves and which is capable of reproducing audio signals therefrom in the absence of a video modulated carrier wave.

One of the features of my invention consists in employing a single wide band channel for translating both video and audio modulated high frequency waves and separating an audio modulated intermediate frequency wave from the video signals subsequent to demodulation of the same and prior to the application of video signals to `a picture tube.

In a modification of the circuit of my invention, an auxiliary oscillator is employed to provide a heterodyning oscillation in the absence of a video carrier so that the receiver may be employed for reception of audio signals during such periods.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims.

' `both as to its organization and method of opera- My invention itself, however,

tion, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which Fig. 1 is a block diagram of a television receiver circuit embodying my invention; Fig. 2 is a detailed circuit diagram of a portion of the receiver circuit of Fig. l; Fig. 3 is a modification of the portion of the receiver circuit of Fig. 2; and Figs. l and 5 are modifications of the receiver circuit of Fig. l.

It is known that the frequencies of carrier waves employed in the transmission of television signals and of audio signals utilized in conjunction with the television signals are established by Government regulations. The frequencies of the picture carrier waves and of the audio or sound carrier Waves are separated in frequency in accordance with such regulations by a frequency of 4.5 vmegacycles, the audio carrier wave being of a higher frequency than the video carrier wave. Thus, for example, a typical television transmitter may employ a carrier wave for the video signals which has a center frequency of 45.25 megacycles. The same television transmitting station will employ a frequency of 4.9.75 megacycles as the frequency of the audio carrier wave.

Referring now to Fig. 1 of the drawing, I have there shown an antenna I which is adapted for receiving a complete television signal comprising both a video signal modulated carrier wave and an audio signal modulated carrier wave. The

' antenna I supplies the received carrier Waves to a rst detector circuit 2 where the received carrier waves are combined, as in a usual supern heterodyne circuit, with high frequency oscillations provided by a local oscillator 3. The detector circuit 2 may include also circuits for amplifying the received waves prior to mixing or heterodyning with the locally generated oscillations. The output of the circuit 2 is supplied to an intermediate frequency amplifier 4 which may comprise one or more stages of amplification and which has a band pass characteristic of sufficient width that both the video intermediate frequency carrier Waves and the audio intermediate frequency carrier waves are amplified and translated by the circuits of the amplifier 4. However, in order not to overmodulate the video carrier and lose contrast range in the received picture, it is desirable that the audio signal be attenuated in the intermediate frequency amplifier prior to detection of the combined signal.`

his may be accomplished by reducing the band Width of the intermediate frequency circuits or in any other Well known manner.

The intermediate frequency carrier Waves for the audio and video signals are separated in frequency byi4.5 megacycles subsequent to the mixing action inthe circuit 2. The ampliiiedintermediate frequency' Waves are rectified in a detector 5 to reproduce the video signal from the video modulated intermediate ,frequency ,vv/laves.

At the same time, due to the curvilinear charac-7:4.

audio.:smodulatedmerrie;l wave are ampliiiedidn wherethe. ermegacyleware ispseparatedffrpm e the-video.' signals, Ereferably, the? lter-11 :i of the -inn'ite attenuating. typeto --thatronlYJ/-l throughq; a volume control potentiometer-4 I gute.

anf=audio amplifier I3 and ultimately speakervld, ..y In the circuito Fig n non. of theaudiof signalsfffrom audio .modulated to a loudpresent.invention.v .Likewisefthe .picture tuloegll1 are.-`customarilyused ingconjunction with Ithe .picture"tubeofV ai television receiver@ s In Fig.v 2, I have shown one circuit arrangef-vv mentbywhich thefaudiq intermediate i.fr{,exholu'elrircy the ivideo signa-lf,translatingcircuits.,v In` tlfiL cuff-.- cuit; the.--.e1ectron discharge device {l-may y aevideo .amplifier havingyan ,anode eircuityv ch.,

includes a resonant-.circuit comprisingjinducttantlfev quency: of 45.5,v meg-acycles.:vr Amd@ potentials, 91." thedevicel lare` supplied through: hey-tumd circuit anda` resistance IBgfrom-aconventional source indicated: by, the legendiB-lf. 'Gonr 1ected across .the inductance is ag series `circuit comprising -a capacitancef [mand a resistanceil0. common terminal of resistance Ztl-and rrduct It is Yconnected-to ground throughaca-p it 2-!.\.-:' If.the;valuesfofshe capacitance c inductance.- t6 are 'suchf;thatf-.they,-1.`4` y c orrnear. thef-requencyfwhich it `is :desiredj to Iattenuate-.finnitelyn that ---is;f' 4.5megacycles, and if the values of resistance. 2li-.and,capacitance-12.! are --properly adjustedxthe currents.ofy vthe fre-r duenoy lwhich vit.- is :desi-redr toy attenuatemand whichflow'throughy resistance 24] to the terminal 2-2gare equalfand oppositeVr to curr-entsof this fre quency which flow through capacitancey yI 9 ....to this termina-11.l *orden to uolctaintsuch. opposif4 tion of the currents which ow through resistor This carrier. Wave.V

Q9 signals' arcirsupplied toga SQGQIld Videcamplifien 20 andY capacitance I9, it has been found that resistance 20 must have a relatively large value compared With the reactive impedance of capacitor 2| at the frequency to be attenuated. 5 By pro-per choice of the constants, the characteristie. of... .the video circuits .may.a1so. be. made substantiauyuat, up to abscess megacycles.

With the foregoing connection and with proper uvalues of the circuit components, waves of the freguencyvointhe `audio modulated intermediate frequencymaves are innitely attenuated by the circuit elements l5, Il, i9-2L As a consequence, video, signals alone-n are supplied through a couplingcapacitor 23 Ato the input electrode of a video amplier 24.....01'1 the other hand, the audio lnodulatedcintermediate frequency carrier waves may be supplied through a coupling capacitor 25 .to,..the amplitude limiter lll. Some form of amplitude limiting is important to eliminate 20 cross modulation otthevaudio b y thenyidedsignal.

Fig.,3..,lhave"shown amodiication of my Y elin'iinated.y ...Ihn 'this .circuiuthere primary; winding!`.n .The Winding-1 .126.- is een:

netted@ the mii'eofitpte Secondary' Winding.. 2l vto supply. primari/voltage .in series with thea twq'halves of.thesecondary Winding; The scc;l Orf-dart Winding fis. ftueedfby means Of .Variable s f Capacitor w23- :The -npposte ends. Ofbihe Wir-1d:

ing .2.1 fare Connected@ eversegdedet .The

it'ors r3 l, A`32'., serially. .connected resistors 33,.

and lar-eef apaciipr. .35 $11911! a .ratio detest@ i5 is .f.0ur.1. l te'. esubstapti irreSpouSivaiO-amrlitilde. variations. Reet/.ed .were endete previde across the resistors 33,134respectivelyyoltg ages :which are mthefrato @thelvltagefin.-

wiwi-andthieupaer-ha1fof Secondary winding. 27V .tovthat in, coil ,2li 'and .the lower half inwind-, V ing 21. The opposite end-of theyvindingl Vis connected-.to grpuedgfthrouehia. .capacitor 36 Audio signals ,Var couplemrom the junction of coiljandlcap itorithroug a coupling capacitor 31toayolumecontrol i .c Inthe circuit-of Fie- A. .I- provide.. anamnesment vby which thetelevision receiver .circuits are available for the receptiongpf frequency modu.

. lated. -audio `signals even When-fa...videocarrier Wave is not received. c Such conditions occuroiten.

inl stand-by periods. cof.` a; .television .transmitter station or invothenperiods -Whenaif videortransf. mitter Aisvnot operating andjit, is desirable that'k audio signalsfmayvstill.be transmitted. Certain 55 portions ...,ofafthiscircuit.arefidenticalfyvith the circuit of Fig. l and have been identified. with corresponding. reference: numer`als..,.' Ehe intermediate --frequency., signals atlthe. output. .Voir ,the

intermediate. frequency..l ampliHier-.Tare supplied. t0 g the cathode of ardod'e detectorf.3$..a1fhecathode.

of detector 39 `is connectedtoground through a `Winding:Mini a-.couplingtransformer .flhe anode of diode .39 is?connectedy .t0- grO-und. through..

a-fload resigaucesii and' tothe @Quit l electod..

` y A Yile lthe.lowericnd. of-thevvvinding 21is connected 4.to `the-anode of amplifier 42 is supplied to the filter 1 where the audio signals are removed and supplied through the limiter I9 to discriminator I I, volume control I2, an audio amplifier I3, and a loudspeaker I4. The video signals are further amplified in the video amplifier 8 and coupled to the cathode 43 of a picture tube 44. A D. C. restorer circuit is connected between the cathode 43 and ground and comprises a diode rectifier 45 and a load resistance 46.

In order that the television circuits are operative to receive signal modulated carrier Waves in the absence of a video carrier wave, I provide an auxiliary oscillator 41 which injects an oscillation of the frequency of the video carrier into the circuit of the detector 39. The oscillator 41 comprises an electron discharge device 48 having its cathode connected to a tap on inductance 49 and its control electrode coupled to the upper terminal of the inductance 49. The inductance 49 is resonated to the frequency of the carrier wave by means of a tuning condenser 50. The anode of the device 48 is connected to ground through a capacitor5l for alternating currents and supplied with operating potential from any suitable source labelled B-lthrough a switch 52. The current in inductance 49 flows through a winding 53 which is coupled to the winding 40 in the circuit of detector 39.

The oscillator 41 is normally rendered inoperative during television reception by a negative bias which is supplied to the control electrode of the device 48 through a resistance 54 and obtained by connection through a resistance 55 across the D. C. restorer circuit of the tube 44. Thus, when the video carrier is not being received, the upper terminal of resistance 46 is substantially at ground potential because the frequency modulated audio signal at 4.5 megacycles has a low amplitude at the picture tube grid due to the use of 4.5 megacycle rejection circuits. However, when video signal is being received, this terminal is at negative potential with respect to ground and this negative potential is applied to the control electrode of electron discharge device 48. As previously stated, the inductance 49 and capacitance 50 are resonated at the frequency of the video intermediate frequency carrier wave to provide in the circuit of the diode 39, in the absence of a received video carrier wave, an oscillation which is heterodyned with the received audio carrier wave. As a result, a 4.5 megacycle intermediate frequency carrier wave frequency modulated with the received audio signals is present in the anode circuit of diode 39 and utilized to operate the loudspeaker I4.

The operation of the oscillator 41 may also be controlled by means of the switch 52. Thus, if it is desired not to supply a biasing potential to the grid of the device 48 from a D. C. restorer circuit, the oscillator may be normally disconnected by means of the switch 52 and allowed to operate only when a video carrier wave is not being received.

In Fig. 5 I have shown a modification of the circuit of Fig. 4 in which an additional coil 56 is coupled to the inductance 4I?. Coil 56, which is in series with an inductance 51, is resonated by a capacitance 58 at the frequency of the video intermediate frequency carrier wave. trol electrode of electron discharge device 48 is connected to ground through resistances 59 and 60. The resistance 69 likewise functions as the load resistance of a rectifier 6I illustrated as a diode connected across the tuned circuit 51, 58.

The con- LIf) G Il

The resistance 60 is bypassed by capacitor 62 for high frequency waves. In this circuit, when a video carrier wave is not received, the oscillator 41 provides an oscillation of the frequency of the video intermediate frequency carrier wave to the coil 40. However, when a video carrier wave is being received, the video intermediate frequency wave is coupled into the coil 56. The waves developed in the tuned circuit 56, 51, 58 are rectified by the diode 6I to develop across resistance 6U a negative potential which is applied through resistance 59 to the control electrode of discharge device 48 to interrupt operation of the oscillator 41. In this manner, the oscillator 41 normally,

' in the absence of a carrier wave, provides a Wave to the diode 39 which is mixed with an audio intermediate frequency wave to provide a 4.5- megacycle audio modulated intermediate frequency wave. However, when the video carrier is received and is above a predetermined level, the diode 6I recties currents of this frequency to provide a bias which interrupts operation of the auxiliary oscillator.

An important advantage of my improved audio system for television receivers is that it assures tuning of the audio together with the video signals and that the audio circuits remain tuned throughout the reception of a television program. In this way,v the constant retuning of the audio circuit which has been required in previous television receivers is avoided. Furthermore, I have found that with my improved system, requirements as to the local oscillator stability are less rigorous than heretofore required for satisfactory operation of the audio circuit of a television receiver. Thus, in a receiver employing my improved circuit, I have found that the local oscillator may be detuned to a considerable extent without adversely affecting the quality of the sound reproduced by the speaker of the receiver.

Another important advantage of my improved television receiver system is that it permits reception of audio signals even when a video carrier wave is not being received. Thus, by providing a wave of the frequency of the intermediate frequency video wave, the intermediate frequency audio wave may -be mixed therewith to permit operation during such periods. At the same time, the adjustable local oscillator 3 permits tuning over a wide range of signals, the frequency of the auxiliary oscillator being the same for any of the selected stations.

A further advantage of my improved television receiver circuit is that it reduces greatly the number of tubes required in a receiver and, hence,

the overall cost of the receiver. At the same time, improved overall operation of the receiver is obtained.

While I have shown and described particular embodiments of my invention, it will occur to those skilled in the art that many changes and modifications may be made without departing from my invention and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a television receiver, -means to receive a picture modulated carrier wave and an audio frequency modulated wave, said carrier waves being separated in frequency by a constant difference/ frequency, means for converting both of said waves to waves of different frequency, a single channel connected to translate both of said con- Verted `Iwaves, meansfaforfrinixing said licon-vented' waves t'o provide an audio frequencynrnodulated carrier Wave'oafrequency equal to' fthe differencev abetween itheifrequencies of said; converted waves; means coupled to :said'channel land operative :in 'the absence of a-received picture car- 'Waueswbeing separatediin frequency by a=coustant dii'erence'v frequency,` #means -for fccnvertingboth saidfcarrier Waves to WaVeso-diierent frequency, aj-fsin'gl'e clfiann'elV connected to translate both of said converted .yi/'avea Ameans ffor .mixing said converted' `waves to provide .-anf'audio vvfrequency modulated Wave of a frequency-.equalto saiddifference trequencyyan oscillator arrangedto .aprovide aan output-Wave, means for supplying said output` ,Wave tosai'd-mixing means, said output Wave-beingfseparated1in frequency from a vreceived audio'frequency,v modulated wave by -said diierence frequencypand means for Ycontrolling said-ioscillator to supplysaid .output Wave tosaid mixing fmeans -:only duringperiods when -said single channel-'does :not Atranslate a converted --pic ture modulatedfvvave.

f3.' En fa televisienareceiver, vkmeans -to'receive a picture :modulated carrier vvave `andfanaudi'o yfrequency f modulated carrier wave, said carrier Waves bein-'gseparated in nfrequency v'by aY 'constant diierenc'e frequency, imeans for converting both said carrier waves vto waves ofdifferent frequency, a'singlechannelfconnecte'd to translate both of said converted Waves, --means vfor mixing lsaid converted `waves rto provide an audio frequency modulated wavefof a `frequency. equal-to-said'difference frequency,-oscillatormeans for vsupplying: ani: output wave to'nsaid mixing: means; said outputs Wavey being separated .in Afrequency from a 'sreceivedraudio 'frequency' Y-inodulatedv Wave by said vdifference frequency, and means forl disabling said 'oscillator 'means during periods of reception of Vva picture 4modulated carrierwave.

'4.1Infa television receiver, means to receive a picture modulated 'carrier Wave and an audio frequency modulated carrier Wave, -said .carrier Waves being separated in frequency vby a constantdiieren'ce frequency, means :forv converting doth said carrier waves towa'ves of diierent frequency,fa single Achannel'connected to translateV -bothxof said'converted waves, means for mixing said converted waves tozprovide an audio frequencyrnodulate'd wave -of-afrequency equal to said difference ifrequencyfan oscillator arranged to-supply an loutput-Wave "to said mixing means, saidfoutput wave Vbeing separated in frequency from a' received; audio frequency modulated wave bysaid difference frequency, and "means forenergi'zingzsaid voscillator only during periodswhen saidfsingle channelfdoes not ytranslate .a convertedpicture'modulated Wave. f

Y GEORGE W. FYLER REFERENQES CITED The following referencesl are v of record in the viile of this patent:

Number Name Date 'f1-,4953470 Farrington May '27, `1924` 1Q`68`L5'64: Wright Aug. '21, 1928y 1735,134 Schroter Nov. 12, 1929.v '1,797,317 "Brand Maiz 24,1 1931' -r2,0561507 r i-.lHies OC',.'6, 1936' 2,186,455 Gldmaik Jan. 9,1940 A2g/03,954? Seeley y .July"'16, 511946' `v2448p908 Parker Sept. 7, 51948 OTHER REFERENCES AProceedings I. R. (page 56) ,February 1946, 

